1. Field of the Invention
The present invention relates to a system and method for controlling mechanically-driven musical instruments, and in particular to a system and method for controlling the drive of solenoid actuators in a mechanically-driven piano or other instrument.
2. Background of the Technology
Beginning with the invention of pneumatically-driven reproducing pianos in the early twentieth century, systems and methods have been developed for recording music played by a human pianist and for reproducing that music on a piano. Many of these systems and methods have attempted to reproduce not only the temporal sequence of notes played by the pianist, but also their dynamics or the sharp contrasts and subtle shadings in loudness that help to make piano performances pleasing. The overall problem of reproducing dynamics can be divided into two distinct parts: recording the dynamics played by a pianist, and recreating these dynamics on a piano.
The problem of recording the dynamics played by a pianist is addressed, for example, in U.S. Pat. No. 4,307,648 to Wayne Stahnke, the entirety of which is incorporated herein by reference. However, there is an unmet need in the art for improved systems and methods for recreating the recorded dynamics.
In an application such as a mechanically-driven piano, recorded music is recreated, for example, using solenoids or other actuators. One solenoid or other actuator is provided for each key of the piano. Each solenoid or other actuator controls the movement of one piano key to recreate recorded music. The solenoids or other actuators may be operated at various speeds to recreate the dynamics of the recorded music.
The solenoids or other actuators are driven, for example, using switching-mode drivers. One switching-mode driver is provided for each solenoid or other actuator, and thus, each switching-mode driver controls one key of the piano. The switching-mode drivers are either fully “on” or fully “off.” When a particular note is not to be played, the switching-mode driver for that note is off.
When a particular note is to be played, the switching-mode driver for that note alternates between the on and off states at a high rate, such as, for example, a rate above the limit of audibility. By controlling the proportion of time the switching-mode driver is turned on, the loudness of the note can be controlled. For example, if a loud note is desired, the switching-mode driver is turned on for a large proportion of the time. The solenoid or other actuator is operated at a relatively fast speed, and a relatively loud note is played. In contrast, if a soft note is desired, the switching-mode driver is turned off for a large proportion of the time. The solenoid or other actuator is operated at a relatively slow speed, and a relatively soft note is played.
In some systems, each switching-mode driver is controlled independently. However, other implementations control two or more switching-mode drivers in synchronism, which reduces the cost. Such a system is described, for example, in U.S. Pat. No. 5,022,301 to Wayne Stahnke, which is incorporated herein by reference in its entirety.
Historically, analog circuitry has been used to generate the control signals for the switching-mode driver. However, the advent of high-speed digital circuitry makes it feasible to control the switching-mode drivers using purely digital circuitry. In one such digital system, a plurality of digital counters is used to control the switching-mode drivers. One digital counter is used to control each key.
However, this system suffers from several shortcomings. First, because one counter is used for each key, the system is complex and costly. Second, counters exhibit limited speed due to the fact that carry signals must be propagated from stage to stage. The limited operating speed of the counters limits the resolution of the switching-mode drivers. This results in a relatively limited number of distinct dynamic levels, thereby limiting the accuracy of the reproduction.
The solenoids or other actuators are driven from a supply voltage that is derived from local power mains. The voltage of the power mains, nominally 117 Volts Alternating Current at 60 Hertz in the United States, actually varies during the course of the day due to varying power demands on the local power distribution system. Local changes in load, such as a change caused by starting household appliances or playing many loud notes at once, can also affect the voltage of the power mains.
In order to obtain a fine musical result, the effect of fluctuations in supply voltage should be reduced or eliminated. Many prior art systems contain a power supply that regulates the supply voltage provided to the solenoids or other actuators. Regulating the supply voltage ensures that a constant voltage is provided to the solenoids or other actuators, and the effect of fluctuations is thereby reduced or eliminated. The power supply used in the prior art systems contains a regulator circuit that is capable of controlling the large currents that appear when many notes are played at once. However, the regulator circuit adds to the complexity and cost of the system.
There is an unmet need in the art for an improved system and method for controlling solenoids or other actuators while reducing complexity and cost. There is a further need to provide a system and method with increased resolution of the switching-mode drivers. There is an unmet need in the art to provide a system that compensates for fluctuations in the supply voltage while reducing complexity and cost. Other problems in music reproduction technology exist.